Sectional tanks for the storage of, for example, water have commonly been made from mild steel and in latter years also from glass reinforced polyester resins (GRP). They are constructed from panels (also known as "shells" or "decks") with flanges which are bolted together with a sealant between each joint. Those made of steel usually have a star pattern embossed in the panel and whilst the earlier GRP tanks had the same pattern later examples have been flat panels. Tanks 4 ft high usually need minimal bracing but tanks 8 ft high and above need external and/or internal bracing to withstand the pressures and deflections encountered when full of water or other liquid.
For ease of construction it is desirable to minimize the number of panels which need to be assembled by using relatively large panels. Typically, for a GRP tank up to 8 ft high, 4 ft square panels may be used. However the larger the panels the less capable they are of withstanding the load of the liquid to be stored and it is therefore necessary, for taller tanks, to use smaller panels, say (2".times.4"), at least for the base and lowermost side panels which will take the greatest load; thus it is necessary in constructing a tall sectional tank to use a large number of small panels or to use panels of different sizes.
Typical weights of 4 ft square tank panels are 70 kg for steel and 30 kg for GRP, a 2.times.4 GRP panel weighing 20 kg. Although GRP panels are preferred because of their lower weight, such panels may undergo deterioration due to the fluid inside the tank (long term contact can cause blistering and moisture ingress into the laminate which causes a breakdown of the glass/resin bond and a lowering of strength).
It is also well known to assemble roofing structures from a plurality of panels of hyperbolic paraboloid shape which are known as "hypar" shells. These are assembled so that their concave surfaces face inwardly of the building of which they form the roof, as illustrated in an article by S. S. Nielsen, I.A.S.S. Bulletin (1981), XXII-1, No. 75, pages 35-44. The effect of long-term deflection of inverted umbrella hyperbolic paraboloid shells has been measured and the results published in an article by Srihari et al, I.A.S.S. Bulletin (1979), XX-1, No. 69, pages 43-48.